A water main that ruptured and created a 40-square-foot hole in a busy set of SoMa intersections threatened to keep commuters on their toes today.

The 100-year-old pipe that pumps millions of gallons of water to customers created an 8-foot-deep pit near 290 Division St. on Saturday night, briefly closing down the 10th Street onramp to northbound Highway 101. Witnesses reported an 8-foot-high geyser as a result of the burst.

Two lanes of Ninth Street were expected to remain closed through today’s evening commute as repair work continues, San Francisco Public Utilities Commission officials said Sunday.

Originally, four intersections — Potrero Avenue and Division Street, Division Street and San Bruno Avenue, Ninth and Brannan streets, and Bryant and 10th streets — and thousands of customers were affected by the burst, which happened about 8:30 p.m. and sent bits of roadway and sediment into faucets. The utilities commission quickly switched several valves in a one-block radius, restoring clean water to the area.

“It was pretty catastrophic,” utilities commission Deputy General Manger Michael Carlin said. “The pipe’s 100 years old. It was cold. It was just its time.”

Most affected was the Thrillpeddlers theater, which is located about 100 feet from the break. Water rose 3 feet above ground and crept to the theater’s indoor stage.

“I was just in the middle of my performance,” producer Russell Blackwood said. “Luckily, we were able to salvage a lot. It’s one of those things that are out of your control.”

About 10 percent of The City’s pipes are just as old as the one that burst, but Carlin said the utilities commission is continuously trying to upgrade the system.

He said this year it has replaced about 9 miles of pipe.

Carlin had no estimate of how much water leaked or how much repairs will cost.